I. Field of the Invention
The present invention relates to dehydration via a closed system.
The present invention relates particularly to a method of and an apparatus for dehydrating biological products including, but not limited to: fruits, vegetables, fish and meat products, by employing a closed system. More particularly, the present invention relates to a method and apparatus for dehydrating such biological products, via a closed system in a manner such that substantially all of the natural moisture of the product is removed while the product retains substantially all of its natural flavors; and fragrances. Moreover, the present invention relates to a method and apparatus of dehydrating such biological products such that the fragrance and flavor of the natural biological product is retained upon rehydration of the dehydrated biological product.
The present invention also relates to dehydrated biological products per se, as well as those made by the above mentioned method of the present invention.
II. Description of the Prior Art
Many methods of, and apparatus for, preserving biological products, in particular food products, are presently utilized and have been known for some time. Each of the prior art methods of preserving for products has serious and significant shortcomings, which it is the object of the present invention to overcome.
Freezing is a commonly utilized method for preserving foods, and various freezing techniques are known in the prior art. In particular, a freezing technique including lyophilization is known in the prior art, particularly from U.S. Pat. No. 5,059,518. Such freezing procedures have several undesirable aspects. These include destructing or destruction of the integrity of the frozen products or materials as well as the need for constant energy expenditure for cooling of the frozen products during storage. Additionally, transportation of the frozen products is more complicated, and the presence of water within the frozen products results in an increase in the total costs for the process.
One of the oldest processes for preserving biological products, and particularly food products, is that of drying or dehydration. From ancient times, it has been known to dry grapes to produce raisins. Such drying processes are, of course, still quite widely practiced today. However, these dehydration or drying processes have serious and significant shortcomings. In particular, since drying processes as utilized today, employ an "open system", the fragrance, flavor and aroma of the product is often significantly changed, during the drying process, from that of the product in its natural state.
The term "open system", designates a drying process or apparatus that operates by utilizing a heated air flow across the surface of the product to be dehydrated and wherein the air flow is not isolated from the ambient atmosphere, but air exchange between the dryer and ambient air is permitted. While in many of these prior art "open systems", some air might be recycled for energy efficiency purposes, the prior art dehydration systems do not utilize a closed system, wherein the entire volume of air utilized for drying of the product is closed-off, isolated, or sealed from the ambient atmosphere and recycled, without exchange of air with the ambient atmosphere during a drying cycle.
Thus, in the prior art drying processes, as the evaporation of moisture from the product proceeds, flavor, fragrance and aroma are also evaporated from the product and are thus not retained in the dehydrated product. Accordingly, the taste, texture, flavor and aroma of a product dehydrated by conventional dehydration process becomes substantially changed as a result of the drying process. Accordingly, dehydrated products produced via the prior art dehydration processes cannot be reconstituted and used as a acceptable substitute for the natural product. Using the grape-raisin example, since the flavor and fragrance of a grape differs significantly from that of a raisin, a raisin is not an acceptable substitute for a grape in processed food products such as, for example ice cream and yogurt.
Other methods of preserving foods by drying include the addition of chemical compounds, such as, for example, trehalose or sulfite.
Additionally, preservation of foods by the addition of sugar during the drying process, while quite old, is still practiced in the art. However, because of the general trend, particularly for health reasons, to avoid the addition of chemicals or extra sugar to food products, these processes have recently become somewhat less desirable than in the past.